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<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.qi.reference.parser_concepts.parser"></a><a class="link" href="parser.html" title="Parser">Parser</a>
</h5></div></div></div>
<h6>
<a name="spirit.qi.reference.parser_concepts.parser.h0"></a>
            <span class="phrase"><a name="spirit.qi.reference.parser_concepts.parser.description"></a></span><a class="link" href="parser.html#spirit.qi.reference.parser_concepts.parser.description">Description</a>
          </h6>
<p>
            The <span class="emphasis"><em>Parser</em></span> is the most fundamental concept. A Parser
            has a member function, <code class="computeroutput"><span class="identifier">parse</span></code>,
            that accepts a first-last <a href="http://en.cppreference.com/w/cpp/named_req/ForwardIterator" target="_top"><code class="computeroutput"><span class="identifier">ForwardIterator</span></code></a> pair and returns
            bool as its result. The iterators delimit the data being parsed. The
            Parser's <code class="computeroutput"><span class="identifier">parse</span></code> member
            function returns <code class="computeroutput"><span class="keyword">true</span></code> if
            the parse succeeds, in which case the first iterator is advanced accordingly.
            Each Parser can represent a specific pattern or algorithm, or it can
            be a more complex parser formed as a composition of other Parsers.
          </p>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl class="variablelist">
<dt><span class="term"><code class="computeroutput"><span class="identifier">p</span></code></span></dt>
<dd><p>
                  A <code class="computeroutput"><span class="identifier">Parser</span></code>.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">P</span></code></span></dt>
<dd><p>
                  A <code class="computeroutput"><span class="identifier">Parser</span></code> type.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">Iter</span></code></span></dt>
<dd><p>
                  a <a href="http://en.cppreference.com/w/cpp/named_req/ForwardIterator" target="_top"><code class="computeroutput"><span class="identifier">ForwardIterator</span></code></a> type.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code>, <code class="computeroutput"><span class="identifier">l</span></code></span></dt>
<dd><p>
                  <a href="http://en.cppreference.com/w/cpp/named_req/ForwardIterator" target="_top"><code class="computeroutput"><span class="identifier">ForwardIterator</span></code></a>. first/last
                  iterator pair.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">Context</span></code></span></dt>
<dd><p>
                  The parser's Context type.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">context</span></code></span></dt>
<dd><p>
                  The parser's Context, or <code class="computeroutput"><span class="identifier">unused</span></code>.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">skip</span></code></span></dt>
<dd><p>
                  A skip Parser, or <code class="computeroutput"><span class="identifier">unused</span></code>.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">attrib</span></code></span></dt>
<dd><p>
                  A Compatible Attribute, or <code class="computeroutput"><span class="identifier">unused</span></code>.
                </p></dd>
</dl>
</div>
<h6>
<a name="spirit.qi.reference.parser_concepts.parser.h1"></a>
            <span class="phrase"><a name="spirit.qi.reference.parser_concepts.parser.valid_expressions"></a></span><a class="link" href="parser.html#spirit.qi.reference.parser_concepts.parser.valid_expressions">Valid
            Expressions</a>
          </h6>
<p>
            In the expressions below, the behavior of the parser, <code class="computeroutput"><span class="identifier">p</span></code>,
            and how <code class="computeroutput"><span class="identifier">skip</span></code> and <code class="computeroutput"><span class="identifier">attrib</span></code> are handled by <code class="computeroutput"><span class="identifier">p</span></code>, are left unspecified in the base
            <code class="computeroutput"><span class="identifier">Parser</span></code> concept. These
            are specified in subsequent, more refined concepts and by the actual
            models thereof.
          </p>
<p>
            For any Parser the following expressions must be valid:
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
<th>
                    <p>
                      Return type
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">p</span><span class="special">.</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> <span class="identifier">l</span><span class="special">,</span> <span class="identifier">context</span><span class="special">,</span> <span class="identifier">skip</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">)</span></pre>
<p>
                    </p>
                  </td>
<td>
                    <p>
                      Match the input sequence starting from <code class="computeroutput"><span class="identifier">f</span></code>.
                      Return <code class="computeroutput"><span class="keyword">true</span></code> if
                      successful, otherwise return <code class="computeroutput"><span class="keyword">false</span></code>.
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="keyword">bool</span></code>
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">p</span><span class="special">.</span><span class="identifier">what</span><span class="special">(</span><span class="identifier">context</span><span class="special">)</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Get information about a Parser.
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">info</span></code>
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.qi.reference.parser_concepts.parser.h2"></a>
            <span class="phrase"><a name="spirit.qi.reference.parser_concepts.parser.type_expressions"></a></span><a class="link" href="parser.html#spirit.qi.reference.parser_concepts.parser.type_expressions">Type
            Expressions</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Description
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">P</span><span class="special">::</span><span class="keyword">template</span> <span class="identifier">attribute</span><span class="special">&lt;</span><span class="identifier">Context</span><span class="special">,</span> <span class="identifier">Iter</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The Parser's expected attribute.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_parser</span><span class="special">&lt;</span><span class="identifier">P</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Metafunction that evaluates to <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>
                      if a certain type, <code class="computeroutput"><span class="identifier">P</span></code>
                      is a Parser, <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>
                      otherwise (See <a href="../../../../../../../../libs/mpl/doc/refmanual/integral-constant.html" target="_top">MPL
                      Boolean Constant</a>).
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.qi.reference.parser_concepts.parser.h3"></a>
            <span class="phrase"><a name="spirit.qi.reference.parser_concepts.parser.postcondition"></a></span><a class="link" href="parser.html#spirit.qi.reference.parser_concepts.parser.postcondition">Postcondition</a>
          </h6>
<p>
            Upon return from <code class="computeroutput"><span class="identifier">p</span><span class="special">.</span><span class="identifier">parse</span></code> the following post conditions
            should hold:
          </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
                On a successful match, <code class="computeroutput"><span class="identifier">f</span></code>
                is positioned one past the last matching character/token.
              </li>
<li class="listitem">
                On a failed match, if a <code class="computeroutput"><span class="identifier">skip</span></code>
                parser is <code class="computeroutput"><span class="identifier">unused</span></code>,
                <code class="computeroutput"><span class="identifier">f</span></code> is restored to
                its original position prior to entry.
              </li>
<li class="listitem">
                On a failed match, if a <code class="computeroutput"><span class="identifier">skip</span></code>
                parser is not <code class="computeroutput"><span class="identifier">unused</span></code>,
                <code class="computeroutput"><span class="identifier">f</span></code> is positioned one
                past the last character/token matching <code class="computeroutput"><span class="identifier">skip</span></code>.
              </li>
<li class="listitem">
                On a failed match, <code class="computeroutput"><span class="identifier">attrib</span></code>
                state is undefined.
              </li>
<li class="listitem">
                No post-skips: trailing <code class="computeroutput"><span class="identifier">skip</span></code>
                characters/tokens will not be skipped.
              </li>
</ul></div>
<h6>
<a name="spirit.qi.reference.parser_concepts.parser.h4"></a>
            <span class="phrase"><a name="spirit.qi.reference.parser_concepts.parser.models"></a></span><a class="link" href="parser.html#spirit.qi.reference.parser_concepts.parser.models">Models</a>
          </h6>
<p>
            All parsers in Spirit.Qi are models of the <span class="emphasis"><em>Parser</em></span>
            concept.
          </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
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